Title : Association of dual decline in gait speed and domain-specific cognition with incident dementia in Japanese older adults: An age-specific cohort study
Background: Previous study found dual decline in gait speed and domain-specific cognition (especially memory) is related with elevated risks of dementia, however, study with a long follow-up period to examine the long-term impact of dual decline on dementia is scared.
Objectives: We aim to understand the declines in domain-specific cognitive function and gait speed in youngest-old adults (65 to 70 years old), and the risk of being dementia until oldest old (85 years old).
Methods: Data were obtained from an on-going age-specific prospective cohort study in Japan called The New Integrated Suburban Seniority Investigation Project. Participants included are those who were about to reach the age of 65 years between 1997 and 2001, and finished health check-ups and self-administered questionnaires at both 65 and 70 years old.
Gait speed decline was defined as subjective speed change from “fast” to “normal” or “slow”, or from “normal” to “slow” in 70-year questionnaire compares to the 65’s. Cognitive tests included the word recall and the delayed word recall from the Alzheimer’s Disease Assessment Scale, the digit span forwards and backwards from Wechsler Adult Intelligence Scale-revised, and the Stroop colour and word test. Cognitive decline was defined as being in the lowest tertile of a 5-year change in each cognitive test. Dementia was diagnosed as the cognitive disability greater than IIa in the Japanese Long-term Care Insurance system. Cox proportional hazard models were used to estimate risk of dementia adjusting for covariates, with death as competing risk.
Results: Among 475 participants (47.8% men), 22.7% progressed to dementia after an average of 12.5-year follow-up. Dual decline in gait with delayed word recall (HR: 3.38, 95% CI: 1.43-7.96), word recall (HR: 2.47, 95% CI: 1.03-5.90), and Stroop colour and word test (HR: 2.64, 95% CI: 1.15-6.05) had higher risks of being dementia than single decline or no decline. The highest risk was found in people with single gait decline in Digit Span Backwards group (HR: 4.52, 95% CI: 1.81-11.29) in competing risk models. Single gait decline was significantly associated with dementia in all five cognitive tests group.
Discussions: Youngest-old dual declines in gait with certain cognitive domains might be a stronger predictor of future incident dementia, however, the single gait decline, even subjective speed decline, still shows a great significance as a low-costing noncognitive marker of dementia from more than a decade ago.